1. Field of the Invention
The present invention relates to an aircraft fuel system equipped with a fuel tank to which nitrogen-enriched air richer in nitrogen than the air is supplied.
2. Description of the Related Art
In a flying aircraft, as the fuel tank is filled with vaporized fuel, it is necessary to prevent the fuel tank from exploding in events such as lightning strikes on the tank or wiring short-circuit. In this connection, an explosion-proof system has been proposed (U.S. Pat. No. 6,547,188). This system supplies the fuel tank with nitrogen-enriched air (hereinafter, NEA), which is higher in nitrogen concentration and lower in oxygen concentration than the air, with bleed air from the engine serving as a gas source.
The outside air pressure changes during ascent and descent of an aircraft. During that time, it is necessary to avoid the fuel tank being subjected to an excessive pressure due to the differential pressure between the outside air pressure and the internal pressure of the fuel tank. It is also necessary to take the air into the fuel tank in an amount corresponding to the volume of the fuel consumed during the flight. For this purpose, the fuel tank has a ventilation function which achieves a balance between the outside air pressure and the tank internal pressure by means of a ventilation channel leading to the outside air.
As the ventilation channel, a left ventilation channel extending in the length direction of the left main wing and a right ventilation channel extending in the length direction of the right main wing are provided. These left ventilation channel and right ventilation channel are each provided with a ventilation port which leads into the fuel tanks in the respective channels.
Here, both the left ventilation channel and the right ventilation channel communicate with the inside of an inner tank located in the fuselage. This arrangement can develop a cross-flow phenomenon of the air blowing through from the left ventilation channel to the right ventilation channel, or from the right ventilation channel to the left ventilation channel.
As the air in cross-flow is supplied into the fuel tank, the NEA supplied in the fuel tank decreases in nitrogen concentration and increases in oxygen concentration.
Increasing the NEA supply capacity to avoid this situation requires a larger amount of bleed air, which increases the amount of air taken into the engine and degrades the fuel efficiency.
Based on the above-described problem, the object of the present invention is to ensure explosion-proof performance without increasing the NEA supply capacity in an aircraft fuel system having a ventilation function.